Open any invoice that has Items listed on it, and then use Ctl Y to see the debits and credits to accounts. This is what you told the data to do for Flow. The sales items typically link to income, which would be a Credit. Sales Taxes, if you have them, Credit a Liability account.
Also, Go to the video tutorials:
Desktop PC program video tutorials
Lastly, open your Items List and right click it. Choose Customize Columns. Bring into your view Account (income link) and Expense account. Make sure the items are similar to what you see in my attachments and in the Sample File. You have Sample Files: from the No Company Open screen, bottom Right. Open "product-based" = Rock Castle Construction and look at their Sales, their Items, their Item Profit reporting, their Financial reports.
Then, tell us what you see about your setup, and let us know if you need more help.
Please see my attachments.